1. Technical Field
The present disclosure relates to semiconductor devices and, more particularly, to a signal generation apparatus generating I/Q signals having a phase difference of 90° and signal generation method, a frequency converting appratus including the signal generation appratus and a frequency converting method, and a receiver including the frequency converting apparatus.
2. Discussion of the Related Art
Generally, a Zero-IF structure and an image-rejection structure which are widely used as a receiver structure characteristically require an In-phase signal, hereinafter an ‘I signal’, and a Quadrature-phase signal, hereinafter a ‘Q signal’. The I signal and the Q signal of the receiver can not have an exact phase difference of 90° according to various effects, such as a manufacturing process, a supply voltage or the temperature. Accordingly, as a signal to noise ratio (SNR) gets lowered, a receiving sensitivity of a receiver drops.
FIG. 1 is a block diagram of a conventional frequency converting apparatus. Refering to FIG. 1, the frequency converting apparatus 10 includes a signal generation circuit 12, a first mixer 18, a second mixer 20, and filters 22, 24.
The signal generation circuit 12 generates the I signals Ip and In and the QA signals Qp and Qn. The signal generation circuit 12 includes a voltage-controlled oscillator 14 and I/Q signal generator 16, the voltage controlled oscillator 14 generates differential signals In+ and In−, the I/Q generator 16 generates the I signals Ip and In and the Q signals Qp and Qn in response to the differential signals In+ and In−. Signals Ip and In are differential signals, signals Qp and Qn are also differential signals and signals Ip and Qp, or signals In and Qn should have a respective phase difference of 90°.
The first mixer 18 mixes a radio input signal RFIN with at least one of the I signals Ip and In and outputs the mixed signal to a filter 22. The filter 22 outputs a first intermediate frequency IIF after filtering an output signal of the first mixer 18.
The second mixer 20 mixes the radio input signal RFIN with at least one of the Q signals Qp and Qn and outputs the mixed signal to a filter 24. The filter 24 outputs a second intermediate frequency QIF after filtering an output signal of the second mixer 20.
When a phase difference is not exactly kept at 90° between the I signal Ip and the Q signal Qp or between the I signal In and the Q signal Qn, an image rejection characteristic of each mixer 18 and 20 can be degraded.
FIG. 2 illustrates a circuit of an I/Q signal generator of the frequency converting apparatus illustrated in FIG. 1. Referring to FIG. 2, the I/Q signal generator 16 generates the I signals Ip and In and the Q signals Qp and Qn in response to the differential signals In+ and In−.
However, when a mismatch occurs between two transistors Q9 and Q10 or Q11 and Q12 composed in a pair, since an operation time becomes different between a first stage for outputting the I signals Ip and In and a second stage for outputting the Q signals Qp and Qn, the phase difference between signals Ip and Qp or signals In and Qn may not be kept at 90° exactly. The first stage includes a plurality of transistors Q1, Q2, Q3, Q4, Q9 and Q10, the second stage includes a plurality of transistors Q5, Q6, Q7, Q8, Q11 and Q12.
Therefore, when an operation speed of the first and the second stage is changed by adjusting at least one of a current I1 and a current I2, the phase of I signal and Q signal is adjusted. But, this method can involve a problem illustrated in FIG. 3.
FIG. 3 is a vector diagram for explaining the problem occurring when the phase difference between output signals of the I/Q signal generator illustrated in FIG. 2 is adjusted to 90°. Refering to FIG. 2 and FIG. 3, the I signal is the same as the Q signal in magnitude, but the phase difference between the I signal and a QA signal larger than 90°. When the QA signal is compensated by changing the operation speed, the phase difference between the I signal and a QC signal may be adjusted to 90°, but there still is a problem that the magnitude of the QA signal is reduced to a size of the QC signal.